Efficient generation and measurement of guided torsional waves using magnetostrictive nickel patches

The guided-wave technology becomes a powerful tool for the non-destructive inspection of cylindrical waveguides. Various wave modes such as longitudinal. torsional, and flexural modes can be used for waveguide inspection, but the non-dispersive first branch of the torsional wave mode is the most attractive. However, the torsional wave is difficult to generate compared to other waves, so it has been used only in limited applications. Motivated by this, we are concerned with the efficient generation and measurement of torsional waves in a waveguide. To generate the torsional wave, a new strip configuration is developed; several pieces of nickel strips are bonded at oblique angles with respect to the pipe axis. The validity of the proposed transducer configuration as well as its good performance is verified through a series of experiments.